The invention relates to a welding head for a strap binding machine including a strap guide element that can be moved into and out of the strap guide path, a welding device that can be moved into and out of the strap guide path and that is for fusing the strap segments of the overlapping strap ends that are to be welded, and a pressing device for pressing the fused strap segments against a pressure part.
Strap binding machines bind packaged goods, for instance a stack of catalogs or newspapers, with a strap such as a stable plastic strap. In order to fix this strap in its taut state about the package, a welding head is provided that makes it possible to join the two overlapping strap ends of the binding strap, which is first fed via an appropriate insertion apparatus into a frame surrounding the package, the frame then being opened and the strap being securely tautened thereabout (for which a tautening system known from the subsequently published German patent application can be used). This occurs in that the strap ends in the overlapping region are locally fused by means of a welding device and are pressed securely against a pressure part by means of a pressing device such that the joint results in the fused region. The manner in which a binding machine works is sufficiently well known, and it is not necessary to go into greater detail about this.
A welding head of the type cited in the foregoing is known for instance from EP 1 076 006. In the welding head described therein, a strap guide part is provided that can move along a horizontal longitudinal guide and guides the strap that has been inserted in the frame during the insertion process. In order to be able to weld the strap ends to one another, it is necessary to move the strap guide part out of the strap guide path prior to the welding process and to position the welding device there in order to fuse the strap ends so that the fused strap segments can then be compressed subsequently. That is, in addition to the strap guide element in the welding head in accordance with EP 1 076 0006, the welding device is also received longitudinally movable in a longitudinal guide in order that it can be displaced between the non-working position and the working position in the strap guide path between the strap ends. The compression occurs by means of a pressing device, which is also longitudinally displaceable but which, in contrast to the horizontally guided strap guide part and the welding device, is however vertically displaceable, and which, after the welding device has been withdrawn from the strap guide path, presses the fused strap segments together against a pressure part.
Thus, overall a plurality of longitudinal guides are provided for the various parts to be moved during a welding process, which is disadvantageous for a number of reasons. First, longitudinal guides are complex by design. Precisely aligned guides and moving parts must be provided so that precise movement is possible. Furthermore, continuous lubrication is necessary in order to be able to assure low-friction movement. It is also disadvantageous that the longitudinal guides frequently become soiled after they are open in general.
The invention is based on the provision of suggesting a welding head that is improved both in terms of design and in terms of function.